GB2109976A

GB2109976A - Display apparatus

Info

Publication number: GB2109976A
Application number: GB08131432A
Authority: GB
Inventors: Martyn Neil Gilbert
Original assignee: Texas Instruments Ltd
Current assignee: Texas Instruments Ltd
Priority date: 1981-10-19
Filing date: 1981-10-19
Publication date: 1983-06-08
Also published as: GB2109976B

Abstract

A display apparatus with a plurality of display elements (7) has data storage means (2) having three output circuits (6, 8, 9) responsive to data stored in corresponding sections (3, 4, 5). Two of the output circuits (6, 8) select the element or elements (7) to be energised and the third output circuit (9) determines a further characteristic of the display. The third output circuit (9) may cause certain of the energised elements (7) to flash on and off, flash a different colour, or produce a display of a different colour from the other energised elements. The third output circuit (9) may also cause a sound to be generated. The display means may be a vacuum fluorescent device, the third output circuit (9) being used to correct non-uniformity due to d.c. energisation of the filament. <IMAGE>

Description

SPECIFICATION Display apparatus This invention relates to display apparatus and in particular to such apparatus including display means with a plurality of areas each of which hays one or more display elements capable of being energised to produce a desired display in the particular area.

Examples of display means are electroluminescent panels, liquid crystal displays, light-emitting diode displays, plasma displays and vacuum fluorescent display tubes. One example of such a display consists of rows of multi-segment characters for producing digital indications of the values of certain variables coupled to the display means.

In co-pending PatentApplication No.81.11391, there is described a data acquisition and display system including a display means of the kind described above in which the data to be displayed is stored in a display random access memory. The display means itself is divided into a plurality of rows and the elements of the display in the rows are regarded as lying in columns. The display RAM is divided into two parts, one part being related to the rows of the display means and the other part to the columns. It will be apparent that each location in the display RAM corresponds to a particular element in the display means and consequently the data stored in the display RAM can be arranged to provide any desired display on the display means.

In the case of monitoring systems in particular, it is frequently required to draw attention to a particular item displayed, for example a temperature lying outside a normal working range of temperatures for a particular piece of equipment or an oil pressure value which lies below a safe value for an internal combustion engine. If the display includes several numbers or other items of information, it is possible that the change of value to one lying outside an acceptable range might not be noticed. It is an object of the present invention therefore to provide means suitable for use in the system described in the above-mentioned co-pending patent application and also applicable to other systems using the same display apparatus which would enable a particular display item to be distinguished from the other display items.

According to the present invention there is provided a display apparatus including a display means having a plurality of areas, each with one or more display elements capable of being energised to produce a desired display in the particular area, a storage means for data to be displayed by the display means, the storage means having a plurality of individually addressable locations, each of which is capable of storing a group of digits, and each group being divided into three parts, the storage means having one or more first output circuits each responsive to a digit of a first part of the groups to apply a first signal to elements of the display means defining a desired display, one or more second output circuits, each responsive to a digit of the second part of the groups to apply a second signal to the element or elements of a respective area of the display means, the elements of the display means being such that they become energised when it receives both the first and second signals, wherein the storage elements also has one or more third output circuits responsive to respective digits of a third part of the groups to produce respective third signals defining a further characteristic of the display to be produced by the display means.

In one example the third signal represents a number which is used to determine the brightness or contrast of the energised display elements against the background. This may be achieved by controlling the duty cycle of the first and/or second signals.

Although, as mentioned above, the display means may be of any of a number of types, in a particular example it is a vacuum fluorescent device and the third signals are used to correct the non-uniformity of the brightness of the display resulting from changes in the bias on the individual elements of the device due to the d.c. energisation dt;the filament.

Alternatively, the third signals may be used to cause the display elements to exhibit a particular colour, different from that of the other elemets, or to flash on and off or to flash with the change of- colour The third signals may additionally be used tON draw attention to the display by causing the generation of a sound.

In order that the invention may be fully understood and carried into effect it will now be described with reference to the accompanying drawings, of which Figure lisa block diagram of one example of display apparatus according to the present invention.

Figures 2 and 3 are respectively side and plan views of part of a vacuum fluorescent display device; Figure 4 is a diagram of a circuit for adjusting the brightness or contrast of a display element relative to its background in response to a number derived from the control field of the display RAM shown in Figure 1; and Figure 5 shows a circuit arrangement without a transformer for providing an a.c. supply to the filament of a vacuum fluorescent device.

Referring now to Figure 1, on the assumption that the display apparatus shown is used to display data acquired by a system of the type described in co-pending patent application No.81.11391, the box 1 represents the data acquisition and control circuits of this system. It should of course be understood that this is only one example of the kind of system which could make use of the display apparatus. The block 2 represents the display random access memory having a plurality of individually addressable locations represented by the rows of the block 2. The addressing circuits for this memory are not shown in Figure 2 but are assumed to be able to address the locations for writing information into them and reading it from them in some suitable manner, for example in serial order.Within the display RAM 2 there are three fields, a data field 3, a multiplex ,0 field 4 and a control field 5. As shown in Figure 1, the data and multiplex 0 fields each have 16 columns and the control field has 8 columns, the columns corresponding respectively to the number of bits of each location allocated to the particular field. This sub-division of the locations into three fields may be arranged in other ways, for example, the data field could have 24 fields, in multiplex 0 field 6 columns, and the control field 10 columns. The output signals obtained from the data field 3 when the different locations of the RAM 2 are read are applied via drive circuits 6 in parallel to the column inputs of a display device 7.Similarly, the output signals from the multiplex 0 field 4 are applied via drive circuits 8 to the row inputs of the display device 7. The outputs of the control field 5 are applied to display control circuits 9 which generate in response to the signals from the control field 5 signals for controlling the drive circuits 6 and 8 which are applied via conductors 10 and 11 respectively.

It should be noted that the display device 7 has as many columns as the data field 3 and as many rows as the multiplex PI field 4 has columns. For other shapes of display means than the square one shown, the numbers of columns in the data field and the multiplex 0 field are modified accordingly.

In one example of the invention, the data stored in the control field 5 is used to regulate the brightness of the display produced on the display device 7, and this is achieved by using certain of the digits from the control field 5 to define the duty cycle of the signals applied to the display device 7 by either or both of the drive circuits 6 and 8. If the energisation of the elements of the display device 7 results in the emission of light from the elements, then the brightness of the display would be able to be modulated by the variation of the duty cycle of the signals from the drive circuits 6 and/or 8. It is assumed that the elements of the display device 7 can only be energised if they receive signals along both the row and the column in which the element lies.

In another example of the invention, the display device 7 includes several arrays of elements interleaved with one another, each array producing a different output colour, and the drive circuits 6 and 8 include gates enabling the different arrays to be energised selectively under control of the display control circuit 9. For example, suppose the display device 7 generated a display of number representing oil pressure, then the display device might include an array of green light producing elements inter leaved with an array of red light producing elements.

If the oil pressure were to fall below a critical value, then a signal from the control field 5 would actuate the control circuit 9 to change the display of the oil pressure from a display in green light to a display in red light, thus drawing attention to the fact that the oil pressure was below the critical value.

As a modification of the arrangements described above, the frequency of the duty cycle may be arranged to be sufficiently low so that the display is caused to flash visibly in response to the output signals from the control circuits 9. Such flashing may be simply on and off or it may involve a change of colour so that the flashing is from red to green, for example.

The display device 7 of Figure 1 may be a vacuum fluorescent device and Figures 2 and 3 represent respectively diagrammatic side and plan views of such a device.

Referring to Figures 2 and 3, the device is basically a multiple tetrode in a flat evacuated envelope of glass, the envelope being represented in Figure 2 by items 20 and 21 respectively representing in crosssection the front and rear faces of the envelope.

Within the envelope there is provided a filament 22 which is in the form of a single wire extending from one end of the envelope to another and possibly traversing the area of the device in zig-zags or meanders. Adjacent to the filament 22 is an accelerator grid 23 and beyond that a number of control grids 24 in the form of strips transverse to the filament 22. Parallel to the filament 22 on the envelope rear face 21 are provided a plurality of anode strips 25, and on the anode strips underneath each of the control grids 24 are located dots 26 of electron bombardment activated phosphor.

In the operation of the device shown in Figures 2 and 3, electrons are emitted from the filament 22 when it is heated by the passage of current through it, and these electrons are drawn by the accelerator grid 23 towards the anode strips 25. If a control grid 24 has a positive bias, the electrons pass through it towards the anode strip 25 and activate the phosphor dots underneath it, provided that the anode strip is also maintained at a positive potential. If, however, a control grid 24 is negatively biassed, the electrons are repulsed by it and do not reach the phosphor dots beneath it. Similarly, if an anode strip is negatively biassed instead of positively biassed, then the electrons are repulsed before reaching the phosphor dots on that strip, so those dots are not energised.It will be apparent therefore that by selectively applying positive and negative biases to the control grid 24 and the anode strip 25 any patterns of phosphor dots can be energised and caused to emit light. Clearly, by modifying the formulation of the different phosphor dots, it would be possible to produce a display able to generate different colours if required.

A difficulty which arises with a vacuum fluorescent device of the type shown in Figures 2 and 3 is that if the filament 22 is heated by the passage of a direct current through it, there will be a voltage drop along the length of the filament corresponding to the voltage necessary to produce the heating current in the filament. This voltage drop will have the effect that the emission of electrons from the more positive parts of the filament will be lower than that from the more negative parts since the bias of the accelerator grid relative to the filament will vary along the length of the filament. As a result of this variation in emission the brightness of the display will vary along the length of the filament. In orderto overcome this, the filament may be heated by means of an alternating voltage of a sufficiently high frequen cy to avoid visible flickering. Alternatively, the data stored in the control field 5 of the display RAM shown in Figure 1 may be arranged to vary the duty cycle of, for example, the drive circuits 8 if the filaments run parallel to the columns of the display device 7 or of the drive circuits 6 if the filaments run parallel to the rows of the display device 7.

In order to achieve control of the duty cycle of the drive circuits in response to a number stored in the control field 5, the circuit arrangement shown in Figure 4 may be employed. In this Figure, the digits Ti, T2 and T3 from the control field 5 are stored in a register 30 and periodically entered into a counter 31 as described below. Clock pulses from a clock 32 are applied via a gate 33 to cause the counter 31 to count downwards, and when the clock in the counter 31 reaches zero it produces an output on a conductor 34 which sets a monostable trigger 35 and is also used to enter again the number represented by the digits T1, T2 and T3 stored in the register 30 into the counter 31. The output of the counter 31 is also applied to reset a bistable trigger 36 which is set by the reset output of the monostable trigger 35.The output of the trigger 36 when set forms the modulated duty cycle of the circuit on a conductor 37 and is also used to open the gate 33.

In the operation of the circuit of Figure 4, the value represented by the digits Ti, T2 and T3 can vary from 0 to 7, and the larger the number the longer is the period for which the output of the trigger 36 is high. Assuming that the monostable 35 has just become reset, the trigger 36 is set and the gate 33 is open whilst the output on the conductor 37 is high.

Clock pulses are applied from the clock 32 to cause the counter 31 to count downwards and clearly the time taken for the counter to reach zero will depend on the number represented by the digits T1, T2, T3.

When the counter 31 reaches zero, the trigger 36 is reset, thus closing the gate 33 and setting the voltage on the conductor 37 to low. At this time, the monostable 35 is set and remains set for a fixed period of time until it resets itself automatically and the cycle re-starts. From a consideration of the above, it will be apparent that the periods for which the voltage on the conductor 37 is low are all of the same duration being determined by the reset time built into the monostable 35. On the other hand, the periods for which the voltage on the conductor 37 is high depend on the number entered into the counter 31.

As mentioned above, one way of avoiding the variation in brightness over a vacuum fluorescent display device due to the variation in bias resulting from the d.c. heating of the filament is to use an alternating supply to heat the filament. However, the application of an alternating voltage to a filament usually requires a transformer and transformers are usually bulky and heavy, particularly in relation to the size and weight of integrated circuits. One way of avoiding the need for a transformer is to use a semiconductor circuit to apply an alternating voltage to the filament, and one example of such a circuit is shown in Figure 5 where the filament is represented at reference 40.The alternating supply is applied to the filament 40 by means of two drive circuits 41 and 42 each consisting of two transistors in series connected from an earth conductor 43 to a conductor 44 maintained at a positive supply voltage Vcc.

The circuits 41 and 42 are operated in push-pull, that is to say with the diagonally opposite transistors in the same conducting state, by outputs from buffer circuits 45. The alternation of the conduction of the transistors in the circuits 41 and 42 defines the frequency of alternation of the current applied to the filament 40 and this of course should be high enough to avoid visible flickering. The switching signals for the transistors of the conductors 41 and 42 are obtained from an oscillator 46 the output of which is divided by two frequency dividers 47 and 48 in series, the second frequency divider 48 providing the drive signals for the buffer circuits 45.

CLAIMS (Filed on 19th Oct 1982) 1. A display apparatus including a display means having a plurality of areas, each with one or more display elements capable of being energised to produce a desired display in the particular area, a storage means for data to be displayed by the display means, the storage means having a plurality of individually addressable locations, each of which is capable of storing a group of digits, and each group being divided into three parts, and, connected to the storage means, one or more first output circuits each responsive to a digit of a first part of the groups to apply a first signal to elements of the display means defining a desired display, and one or more second output circuits, each responsive to a digit of the second part of the groups to apply a second signal to the element or elements of a respective area of the display means, the elements of the display means being such that they become energised when they receive both the first and second signals, wherein the storage elements also have one or more third output circuits responsive to respective digits of a third part of the groups to produce respective third signals defining a further characteristic of the display to be produced by the display means.

2. Apparatus according to claim 1 further including a display control circuit responsive to the third signals to control one or both of the first and second signals.

3. Apparatus according to claim 2 wherein the third signal represents a number used by the display control circuit to control the duty cycle of one or both of the first and second signals, thereby to control the brightness or contrast of the energised display elements against the background.

4. Apparatus according to claim 3 including a counter into which the number represented by the third signal is entered, a source of clock pulses, means responsive to number in the counter not being equal to a particular value to permit the application of clock pulses to the counter so as to cause it to count towards the value, and means for producing an output signal for the time interval for which the clock pulses are applied to the counter, whereby the duty cyle of the output signal depends on the number represented by the third signal.

5. Apparatus according to claim 2,3 or 4 wherein the display means is a vacuum fluorescent device and the third signals are used to control the first and/or second signals to correct non-uniformity of the brightness of energised elements of the display arising from changes in the bias on individual

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. parallel to the rows of the display device 7. In order to achieve control of the duty cycle of the drive circuits in response to a number stored in the control field 5, the circuit arrangement shown in Figure 4 may be employed. In this Figure, the digits Ti, T2 and T3 from the control field 5 are stored in a register 30 and periodically entered into a counter 31 as described below. Clock pulses from a clock 32 are applied via a gate 33 to cause the counter 31 to count downwards, and when the clock in the counter 31 reaches zero it produces an output on a conductor 34 which sets a monostable trigger 35 and is also used to enter again the number represented by the digits T1, T2 and T3 stored in the register 30 into the counter 31. The output of the counter 31 is also applied to reset a bistable trigger 36 which is set by the reset output of the monostable trigger 35.The output of the trigger 36 when set forms the modulated duty cycle of the circuit on a conductor 37 and is also used to open the gate 33. In the operation of the circuit of Figure 4, the value represented by the digits Ti, T2 and T3 can vary from 0 to 7, and the larger the number the longer is the period for which the output of the trigger 36 is high. Assuming that the monostable 35 has just become reset, the trigger 36 is set and the gate 33 is open whilst the output on the conductor 37 is high. Clock pulses are applied from the clock 32 to cause the counter 31 to count downwards and clearly the time taken for the counter to reach zero will depend on the number represented by the digits T1, T2, T3. When the counter 31 reaches zero, the trigger 36 is reset, thus closing the gate 33 and setting the voltage on the conductor 37 to low. At this time, the monostable 35 is set and remains set for a fixed period of time until it resets itself automatically and the cycle re-starts. From a consideration of the above, it will be apparent that the periods for which the voltage on the conductor 37 is low are all of the same duration being determined by the reset time built into the monostable 35. On the other hand, the periods for which the voltage on the conductor 37 is high depend on the number entered into the counter 31. As mentioned above, one way of avoiding the variation in brightness over a vacuum fluorescent display device due to the variation in bias resulting from the d.c. heating of the filament is to use an alternating supply to heat the filament. However, the application of an alternating voltage to a filament usually requires a transformer and transformers are usually bulky and heavy, particularly in relation to the size and weight of integrated circuits. One way of avoiding the need for a transformer is to use a semiconductor circuit to apply an alternating voltage to the filament, and one example of such a circuit is shown in Figure 5 where the filament is represented at reference 40.The alternating supply is applied to the filament 40 by means of two drive circuits 41 and 42 each consisting of two transistors in series connected from an earth conductor 43 to a conductor 44 maintained at a positive supply voltage Vcc. The circuits 41 and 42 are operated in push-pull, that is to say with the diagonally opposite transistors in the same conducting state, by outputs from buffer circuits 45. The alternation of the conduction of the transistors in the circuits 41 and 42 defines the frequency of alternation of the current applied to the filament 40 and this of course should be high enough to avoid visible flickering. The switching signals for the transistors of the conductors 41 and 42 are obtained from an oscillator 46 the output of which is divided by two frequency dividers 47 and 48 in series, the second frequency divider 48 providing the drive signals for the buffer circuits 45. CLAIMS (Filed on 19th Oct 1982)

1. A display apparatus including a display means having a plurality of areas, each with one or more display elements capable of being energised to produce a desired display in the particular area, a storage means for data to be displayed by the display means, the storage means having a plurality of individually addressable locations, each of which is capable of storing a group of digits, and each group being divided into three parts, and, connected to the storage means, one or more first output circuits each responsive to a digit of a first part of the groups to apply a first signal to elements of the display means defining a desired display, and one or more second output circuits, each responsive to a digit of the second part of the groups to apply a second signal to the element or elements of a respective area of the display means, the elements of the display means being such that they become energised when they receive both the first and second signals, wherein the storage elements also have one or more third output circuits responsive to respective digits of a third part of the groups to produce respective third signals defining a further characteristic of the display to be produced by the display means.

elements due to d.c. energisation of the filament of the device.

6. Apparatus according to any of claims 1 to 4 wherein the third signals are used to cause certain of the energised display elements to exhibit a colour different from that of the other energised elements.

7. Apparatus according to any of claims 1 to 4 and 6 wherein the third signals are used to cause certain of the energised display elements to flash on and off or to flash with a change of colour.

8. Apparatus according to claim 6 or 7 wherein the display means includes display elements which when energised produce a display of one colour interspersed with other display elements which when energised produce a display of another colour.

9. Apparatus according to claim 6,7 or 8 wherein the display means is a vacuum fluorescent device and there is provided a semiconductor a.c. voltage generator connected to energise the filament of the device.

10. Apparatus according to any preceding claim further including sound generating means and wherein the third signals are also used to cause the generation of a sound.

11. A display apparatus substantially in accordance with any embodiment described herein with reference to the accompanying drawings.